This would be something I would take to the bike shop. Also you might need to have your rear derailleur re-tuned.
My bike came stock with an 11-34 9 speed and to be honest with you i don't think it climbs all that might better than my road bike that had a 12-25 on it. Sure it's easier to pedal but it weighs a ton, suffers from chain slap like no other, and frankly the granny gear is so easy to pedal...well if you went much slower you'd be going backwards. I got a price quote of $55 installed for an identical cassette from my LBS, I'm in the process of building up a new wheel set and I liked the idea of hot swappable wheels. 700 x 32 for commuting, off road, and touring, light rims and 700 x 25's for 'go fast(er)' mode.
Personally I would work on the motor before tossing money into a perceived problem. Train up as best as you can then go give it hell. You'll likely be just fine without a wacky gear combo.